Photoredox Catalysis with Spin Magnetic Field Effects: A Scheme for Chiral Resolution.

Area of Science:

• Spin chemistry
• Photoredox catalysis
• Molecular chirality

Background:

• Magnetic fields and orbital angular momentum break symmetries, linking molecular chirality to magnetic fields.
• Effects like magneto-chiral dichroism and chirality-induced spin selectivity (CISS) are observed but often require amplification for bulk enantioseparation.
• The magnetic field effect on photogenerated radical pairs also breaks time-reversal symmetry.

Purpose of the Study:

• To demonstrate harnessing the magnetic field effect on photogenerated radical pairs for enantiopurification.
• To explore the collective decay of singlet and triplet radical-pair states enabled by magnetic fields.
• To achieve chiral resolution via spin chemistry principles in photoredox catalysis.

Main Methods:

• Utilizing the magnetic field effect on photogenerated radical pairs.
• Leveraging the collective decay of singlet and triplet radical-pair states.
• Employing an axially chiral binaphthyl derivative and a borane photosensitizer as a prototype system.

Main Results:

• Predicted an enantiomeric excess (e.e.) of 90% at steady state within milliseconds.
• Demonstrated constructive interference in singlet and triplet decay channels due to opposite spin-orbit coupling signs in enantiomers.
• Showcased regimes of perfect enantioselectivity (100% e.e.) through chemical optimization.
• Achieved dynamic kinetic chiral resolution via excited-state chirality inversion.

Conclusions:

• The magnetic field effect on radical pairs offers a powerful, untapped control mechanism for enantiopurification.
• Spin chemistry principles provide a novel route for chiral resolution in photoredox catalysis.
• Further optimization of photosensitizers can lead to perfect enantioselectivity.